Flare Stack Thermal Radiation & Dispersion Safety Screener

Under ambient crosswinds, momentum-dominated flare jets bend downwind, displacing the center of radiance closer to grade. The flame length ($L$) and deflection angle ($\theta$) are derived from the momentum ratio between the tip exit jet velocity ($v_{\text{tip}}$) and crosswind speed ($U_w$): $$L = 0.00607 \cdot (Q_{\text{watts}})^{0.478}$$ $$\tan \theta = \frac{U_w}{v_{\text{tip}}} \cdot \left( \frac{\rho_{\text{air}}}{\rho_j} \right)^{0.5}$$ The effective center of radiance is positioned at distance $L/2$ along the deflected flame axis. Flare tip gas exit velocity must be strictly maintained below **Mach 0.50 for emergency relief** and **Mach 0.20 for continuous flaring** to prevent flame lift-off and extreme acoustic vibration.

API Standard 521 Table 7 establishes clear allowable radiant heat exposure thresholds: * **$K \le 1.58\text{ kW/m}^2$ ($500\text{ Btu/h}\cdot\text{ft}^2$):** Continuous exposure permitted for general personnel without specialized protective clothing. Defines the plant sterile exclusion radius. * **$K \le 4.73\text{ kW/m}^2$ ($1500\text{ Btu/h}\cdot\text{ft}^2$):** Permitted for operations requiring slow evacuation (escape time several minutes) with standard cotton work clothing. * **$K \le 6.31\text{ kW/m}^2$ ($2000\text{ Btu/h}\cdot\text{ft}^2$):** Rapid escape required within 1 minute with appropriate workwear. * **$K \le 9.46\text{ kW/m}^2$ ($3000\text{ Btu/h}\cdot\text{ft}^2$):** Emergency evacuation within 5–10 seconds; causes skin blistering within 5 seconds.